Fuses, and methods of forming and using fuses

ABSTRACT

Some embodiments include a fuse having a tungsten-containing structure directly contacting an electrically conductive structure. The electrically conductive structure may be a titanium-containing structure. An interface between the tungsten-containing structure and the electrically conductive structure is configured to rupture when current through the interface exceeds a predetermined level. Some embodiments include a method of forming and using a fuse. The fuse is formed to have a tungsten-containing structure directly contacting an electrically conductive structure. An interface between the tungsten-containing structure and the electrically conductive structure is configured to rupture when current through the interface exceeds a predetermined level. Current exceeding the predetermined level is passed through the interface to rupture the interface.

TECHNICAL FIELD

Fuses, and methods of forming and using fuses.

BACKGROUND

Some types of integrated circuitry utilize fuses. A fuse is a structurewhich can be broken down or blown in response to a predetermined currentflow to interrupt a circuit.

A continuing goal of integrated circuit fabrication is to reduce processsteps. Thus, it would be desirable to develop integrated circuit fuseswhich can be readily incorporated into existing fabrication processeswithout introduction of numerous new steps and materials. Someintegrated circuit constructions may comprise memory arrays, such asarrays of phase change random access memory (PCRAM). It would bedesirable to develop fuse architectures which can be readilyincorporated into existing fabrication process utilized for producingPCRAM.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates an example embodiment fuse (indiagrammatic cross-sectional view) at two different operational states.

FIGS. 2 and 3 are a top view and a diagrammatic cross-sectional view ofan example embodiment fuse. FIG. 3 is along the line 3-3 of FIG. 2, andFIG. 2 is from the orientation shown along the line 2-2 in FIG. 3.

FIGS. 4 and 5 are a top view and a diagrammatic cross-sectional view ofan example embodiment fuse. FIG. 5 is along the line 5-5 of FIG. 4, andFIG. 4 is from the orientation shown along the line 4-4 in FIG. 5.

FIGS. 6-8 are a top view and a pair of diagrammatic cross-sectionalviews of an example embodiment fuse. FIG. 7 is along the lines 7-7 ofFIGS. 6 and 8, FIG. 8 is along the lines 8-8 of FIGS. 6 and 7, and FIG.6 is from the orientation shown along the lines 6-6 in FIGS. 7 and 8.

FIG. 9 diagrammatically illustrates a plan view of a semiconductorconstruction comprising a fuse region and a memory array region.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In some embodiments, the invention includes fuses formed by providing anelectrically conductive structure directly against a tungsten-containingstructure. In some embodiments, the electrically conductive structuremay be a titanium-containing structure. An interface where theelectrically conductive structure joins the tungsten-containingstructure is configured to rupture when current through such interfaceexceeds a predetermined level.

Some embodiments include fuses that may be readily incorporated intoexisting integrated circuit fabrication. The fuses utilize materialswhich are already commonly utilized in integrated circuits. Forinstance, the fuses having titanium-containing structures andtungsten-containing structures may be readily incorporated into existingPCRAM fabrication processes. Specifically, PCRAM already commonlyutilizes titanium-containing structures as heaters within memory cells,and already commonly utilizes tungsten-containing structures asconductive interconnects between circuit components.

Example embodiments are described with reference to FIGS. 1-9.

Referring to FIG. 1, a fuse construction 10 is shown in two differentoperational modes “A” and “B.”

The fuse construction comprises an electrically conductive structure 12over a tungsten-containing structure 14.

The electrically conductive structure 12 may comprise any suitableelectrically conductive composition, and in some embodiments may be atitanium-containing structure. The structure 12 comprises a material 16.Such material may be of any suitable composition; and in someembodiments may comprise, consist essentially of, or consist of amixture of titanium and nitrogen. For instance, the material 16 maycomprise, consist essentially of, or consist of titanium nitride; eitheralone, or in combination with one or more dopants selected from thegroup consisting of aluminum, silicon and carbon.

The tungsten-containing structure 14 comprises a material 18. Suchmaterial may be of any suitable composition; and in some embodiments maycomprise, consist essentially of, or consist of tungsten. Thetungsten-containing structure may be over a semiconductor base (notshown). Such semiconductor base may comprise silicon, and thetungsten-containing structure may join to the silicon through a tungstensilicide interface (not shown).

If the tungsten-containing structure 14 is over a semiconductor base,the construction 10 may be considered to be comprised by a semiconductorsubstrate. The terms “semiconductive substrate,” “semiconductorconstruction” and “semiconductor substrate” mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials), and semiconductive materiallayers (either alone or in assemblies comprising other materials). Theterm “substrate” refers to any supporting structure, including, but notlimited to, the semiconductor substrates described above.

The operational mode “A” has the electrically conductive structure 12directly against the tungsten-containing structure 14. The structure 12joins to the tungsten-containing structure 14 at an interface 20. Suchinterface is configured to rupture when current through the interfaceexceeds a predetermined level. The amount of current suitable togenerate such rupture may depend on, among other things, the compositionof tungsten-containing structure 14 along the interface, the compositionof structure 12 along the interface, and the area of the interface.Thus, the fuse may be tailored for particular applications by adjustingone or more of the composition of structure 12, the composition oftungsten-containing structure 14, and the area of interface 20.

The amount of current suitable to generate the rupture may also dependon the voltage provided across interface 20, but such voltage may berelatively fixed by operational characteristics of an integratedcircuit. Accordingly, the voltage may not be an operational parameterwhich can be readily modified for tailoring operational performance ofthe fuse.

The amount of current suitable to rupture the interface will beinversely related to the area of the interface. In some embodiments, itwill be desired to have the fuse be readily broken with a current lessof than or equal to about 3 milliamps. In such embodiments, the totalarea of the interface 20 may be less than or equal to about 1500 squarenanometers (i.e., nm²), which can enable the fuse to be broken with acurrent of less than or equal to about 2.5×10⁻³ amps under a voltage ofless than or equal to about 2 volts. Thus, in some embodiments thepredetermined current which ruptures the interface may be less than orequal to about 3 milliamps, and may be, for example, about 2.5milliamps.

In some embodiments, the electrically conductive structure 12 maycomprise titanium nitride doped with one or more of silicon, aluminumand carbon. The amount of current suitable to rupture the interface maybe related to the type of dopant and the amount of dopant. Thus,operational characteristics of fuse construction 10 may be tailored, tosome extent, through the selection of dopant concentration and typeprovided within the titanium nitride.

The fuse construction 10 is transitioned from the operational mode “A”to the operational mode “B” by providing sufficient current throughinterface 20 to rupture such interface and thus form the void 22 shownin the operational mode “B.”

The fuse construction 10 is diagrammatically illustrated to be providedbetween circuitry 30 and circuitry 32. The operational mode “A” may beconsidered to comprise a closed circuit through fuse construction 10 sothat the circuitry 30 is electrically connected to the circuitry 32through the fuse construction, and the operational mode “B” may beconsidered to comprise an open circuit through the fuse construction sothat the circuitry 30 is no longer connected to the circuitry 32.

In some embodiments, the rupture of the interface 20 of the fuse occursthrough a mechanism utilizing electron wind. Specifically, current flowthrough the interface causes electro-migration wherein momentum ofmoving electrons causes atoms to move from their original positions, andultimately causes formation of the void 22. The mechanism is providedherein to assist the reader in understanding the invention, and is notto limit the invention except to the extent, if any, that such mechanismis expressly recited in the claims that follow.

The transition from operational mode “A” to operational mode “B” isdiagrammatically illustrated with an arrow 33. Another arrow 34 is shownin dashed-line to indicate that there may be a transition fromoperational mode “B” back to operational mode “A,” which may be utilizedto reset the fuse in some embodiments. Specifically, if sufficientvoltage is provided across the void 22 in operational mode “B,” and ifsuch voltage is provided in an appropriate orientation so that currentmay be flowed across the void in an opposite direction (i.e., anopposite polarity) to the current flow that created the void, then itmay be possible to recover the interface 20 of operational mode “A.” Inthe embodiment discussed above in which the total area of the interface20 was less than or equal to about 1500 nm², the interface could berecovered with a voltage exceeding about 6 volts.

A difficulty in recovering the interfaces of fuse constructions of thetype shown in FIG. 1 is that there may be a substantial variabilitybetween seemingly identical fuses relative to the amount of voltagerequired to accomplish such recovery. Another difficulty is that theremay be substantial differences between the recovered fuses relative tothe current flow across the reestablished interfaces. Regardless of theabove-described difficulties, there may be embodiments in which it isadvantageous to recover at least some of the fuses utilized in anintegrated circuit.

The fuse construction 10 of FIG. 1 may have any suitable configuration.Example configurations are described with reference to FIGS. 3-8.

Referring to FIG. 3, an example configuration 10 a is shown in top view(FIG. 2) and cross-sectional side view (FIG. 3). The constructioncomprises an electrically conductive structure 12 a (which may be atitanium-containing structure) configured as a substantially cylindricalpedestal, and comprises a tungsten-containing structure 14 a which isalso configured to be substantially cylindrical. The tungsten-containingstructure 14 a has a substantially circular end 40, and the pedestal 12a has an edge 41 which is directly against such end. In the shownembodiment, the edge 41 is a substantially circular end of the pedestal12 a.

In the shown embodiment of FIGS. 2 and 3, the end 40 of thetungsten-containing structure 14 a is larger than the end 41 of thestructure 12 a. In other words, the end 40 has a first total area (i.e.,a first surface area), and the end 41 has a second total area (i.e., asecond surface area); with the second total area being less than thefirst total area.

Referring to FIGS. 4 and 5, an example configuration 10 b is shown intop view (FIG. 4) and cross-sectional side view (FIG. 5). Theconstruction comprises an electrically conductive structure 12 b (whichmay be a titanium-containing structure) configured as a substantiallycylindrical annular structure, and comprises a substantially cylindricaltungsten-containing structure 14 b. The tungsten-containing structure 14a has a substantially circular end 45, and the pedestal 12 b has anannular edge 47 which is directly against such end. In the shownembodiment, the edge 47 is a substantially circular end of the annularstructure 12 b.

Referring to FIGS. 6-8, an example configuration 10 c is shown in topview (FIG. 6) and in a pair of cross-sectional side views (FIGS. 7 and8). The construction comprises a substantially cylindricaltungsten-containing structure 14 c having a substantially circular end49. The construction 10 c also comprises an electrically conductivestructure 12 c (which may be a titanium-containing structure) configuredto comprise a plate 50 oriented to have an edge 53 directly against theend 49 of the tungsten-containing structure 14 c; and to have a ledge 51along the plate 50 and also along the end 49 of the tungsten-containingstructure 14 c.

As discussed above, an advantage of the fuse constructions describedherein may be that such fuse constructions can be readily incorporatedinto existing integrated circuit fabrication processes. FIG. 9illustrates an example integrated circuit 70 which may be configured toutilize fuses of the types described above with reference to FIGS. 1-8.The circuit 70 comprises a memory array region 72 and a fuse region 74(which may be referred to as a fuse bank). The memory array region maybe configured to comprise any of numerous types of memory constructions,either now known or yet to be developed. In some embodiments, the memoryarray region may comprise PCRAM. Such memory may utilize titaniumnitride-containing structures as heaters of individual memory cells, andmay utilize tungsten-containing structures as electrical interconnects,in accordance with conventional processing.

The utilization of one or more constructions of the types describedabove with reference to FIGS. 1-8 may enable one or more components ofsuch fuses to be formed simultaneously with one or more components ofthe memory. For instance, tungsten-containing structures of the fusesmay be formed simultaneously with electrical interconnects of the memoryand/or titanium-containing structures of the fuses may be formedsimultaneously with heater structures of PCRAM cells. Such mayadvantageously enable fuses to be incorporated into existing integratedcircuitry without addition of materials or masking steps beyond thosealready utilized in fabrication of the integrated circuitry. Although itmay be advantageous for the fuses to be patterned utilizing a commonmask as that utilized for forming a memory array in some embodiments, inother embodiments it may be preferred to utilize at least one dedicatedmask during fabrication of the fuses (for instance, if it is desired toimplant dopant into the fuses which is not utilized in the memory).

Although the embodiment of FIG. 9 refers to the integrated circuitry 72as being memory, in other embodiments other types of integratedcircuitry may be utilized in combination with one or more of the fusetypes described above with reference to FIGS. 1-8.

The fuses discussed above may be incorporated into electronic systems.Such electronic systems may be used in, for example, memory modules,device drivers, power modules, communication modems, processor modules,and application-specific modules, and may include multilayer, multichipmodules. The electronic systems may be any of a broad range of systems,such as, for example, clocks, televisions, cell phones, personalcomputers, automobiles, industrial control systems, aircraft, etc.

The particular orientation of the various embodiments in the drawings isfor illustrative purposes only, and the embodiments may be rotatedrelative to the shown orientations in some applications. The descriptionprovided herein, and the claims that follow, pertain to any structuresthat have the described relationships between various features,regardless of whether the structures are in the particular orientationof the drawings, or are rotated relative to such orientation.

The cross-sectional views of the accompanying illustrations only showfeatures within the planes of the cross-sections, and do not showmaterials behind the planes of the cross-sections in order to simplifythe drawings.

When a structure is referred to above as being “on” or “against” anotherstructure, it can be directly on the other structure or interveningstructures may also be present. In contrast, when a structure isreferred to as being “directly on” or “directly against” anotherstructure, there are no intervening structures present. When a structureis referred to as being “connected” or “coupled” to another structure,it can be directly connected or coupled to the other structure, orintervening structures may be present. In contrast, when a structure isreferred to as being “directly connected” or “directly coupled” toanother structure, there are no intervening structures present.

Some embodiments include a fuse comprising a tungsten-containingstructure and an electrically conductive structure directly contactingthe tungsten-containing structure. An interface between thetungsten-containing structure and the electrically conductive structureis configured to rupture when current through said interface exceeds apredetermined level.

Some embodiments include a fuse comprising a tungsten-containingstructure having a first end with a first total area, and anelectrically conductive structure having a second end with a secondtotal area. The second total area is less than the first total area. Anentirety of the second end directly contacts the first end. An interfacebetween the first and second ends is configured to rupture when currentthrough said interface exceeds a predetermined level. The electricallyconductive structure may be a titanium-containing structure comprising amixture containing titanium and nitrogen. The interface comprises anarea of less than or equal to about 1500 nm².

Some embodiments include a method of forming and using a fuse. A fuse isformed to comprise a tungsten-containing structure directly contacting atitanium-containing structure. An interface between thetungsten-containing structure and the titanium-containing structure isconfigured to rupture when current through said interface exceeds apredetermined level. Current exceeding the predetermined level is passedthrough the interface to rupture the interface.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

We claim:
 1. A fuse, comprising: a tungsten-containing structure; anelectrically conductive structure directly contacting thetungsten-containing structure; an interface between thetungsten-containing structure and the electrically conductive structurebeing configured to rupture when current through said interface exceedsa predetermined level; the electrically conductive structure being atitanium-containing structure; and wherein the tungsten-containingstructure is a substantially cylindrical structure, and wherein thetitanium-containing structure comprises a plate oriented to have an edgedirectly against a substantially circular end of the cylindricalstructure.
 2. The fuse of claim 1 wherein the titanium-containingstructure further comprises a ledge along the edge, with the ledge alsobeing directly against the substantially circular end of the cylindricalstructure.
 3. A fuse, comprising: a tungsten-containing structure havinga first end with a first total area; an electrically conductivestructure having a second end with a second total area, the second totalarea being less than the first total area; an entirety of the second enddirectly contacting the first end; an interface between the first andsecond ends being configured to rupture when current through saidinterface exceeds a predetermined level; the interface comprising anarea of less than or equal to about 1500 nm²; wherein the electricallyconductive structure is a titanium-containing structure comprising amixture containing titanium and nitrogen; wherein thetungsten-containing structure is a substantially cylindrical structure;and wherein the first end is a substantially circular end of thesubstantially cylindrical structure.